If you challenge a parking ticket, you risk losing the reduction in penalty that paying half swiftly allows.

BBC: Parking - Your Thoughts

Parking is also a challenge.

BBC: Escape from New York

While lining up beer, music and a parking lot isn't usually a problem, finding enough unwanted tomatoes near major cities can be a challenge.

WSJ: Messy Business: Now You Can Pay To Get Hit by a Tomato